Specific antibody deficiency
Other Names: Immunodeficiency due to selective anti-polysaccharide antibody deficiency; Impaired polysaccharide responsiveness; Selective antibody deficiency with normal immunoglobulins; Partial antibody deficiency
Immunodeficiency due to selective anti-polysaccharide antibody deficiency is characterized by normal immunoglobulin levels (including IgG sub-classes) but impaired polysaccharide responsiveness (IPR).
Epidemiology[edit | edit source]
Although the prevalence is not really known, around 100 cases have been reported in the literature, indicating that this syndrome is a rare primary immunodeficiency. Approximately 60% of patients are male.
Cause[edit | edit source]
This immunodeficiency is likely heterogeneous with multiple causes. Genetic factors may play a role, as indicated by the observation of a higher prevalence in certain ethnic populations and of some familial cases. Several hypotheses have been proposed concerning the cause of the disease, but the most likely is a defect in splenic marginal zone B cells. Indeed, polysaccharide antigens are concentrated and presented to B cells by the dendritic cells within the spleen marginal zone. In favour of this hypothesis is the observation of an impaired polysaccharide antibody response in splenectomized patients.
Signs and symptoms[edit | edit source]
The onset of the disease generally occurs during childhood, between 2 to 7 years of age. Patients suffer from recurrent bacterial infections, mostly of the respiratory tract. The offending bacteria are those with a polysaccharide capsule, such as pneumococci, Hemophilus influenzae, meningococci and group B streptococci. Sepsis and meningitis occur less frequently. Allergic manifestations are observed in half of the patients.
Diagnosis[edit | edit source]
The diagnosis is established by identifying deficient antibody response to polysaccharide antigens (usually Haemophilus influenzae b vaccine) contrasting with normal immunoglobulin (including the IgG subclasses) levels and unaffected antibody production to protein antigens (tetanus toxoid, diphtheria). As most children under 2 years of age have a physiological defect in response to polysaccharide antigens, the diagnosis cannot be assessed before this age.
Differential diagnosis The differential diagnosis should exclude other primary immunodeficiencies also characterized by a defective response to polysaccharide antigens, essentially the IgG2-IgG4 deficiency. A defect in antibody production to polysaccharides may be associated with the Wiskott-Aldrich syndrome or Common Variable Immuno Deficiency (CVID). Recently, an adult patient with Btk-deficiency has been reported as only affected by impaired polysaccharide responsiveness.
Treatment[edit | edit source]
Besides their use for controlling infections, antibiotics should also be given as a prophylactic treatment. Immunoglobulin substitution could also be of benefit whenever prophylactic antibiotherapy fails. Vaccination with the conjugate antipneumococcal vaccine is also required.
Prognosis[edit | edit source]
Under treatment, infections are generally well controlled. However, patients should be carefully followed-up since this condition can evolve into a more severe immunodeficiency (IgG subclass deficiency or CVID).
NIH genetic and rare disease info[edit source]
Specific antibody deficiency is a rare disease.
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